Extreme Thermophilia in a Central Australian Ant, Melophorus bagoti

Abstract

The central Australian ant Melophorus bagoti is active during the hottest periods of the summer day. Despite soil surface temperatures exceeding 70° C and air temperatures at ant height exceeding 50° C, this species did not cease midday activity. Individuals were able to survive 2.5 min under these conditions without thermal respite. During natural foraging activity, however, thermal refuges were used during the hottest times of the day. In the laboratory the ants were found to have a critical thermal maximum (CTMax) of 56.7° C and were able to survive for 1 h at 54° C Peak activity in the field occurred when soil surface temperature was 60° C and air temperatures at ant height and ant body temperatures were both 46° C. Apart from being one of the most thermally tolerant animals known, M. bagoti is unique in its avoidance of "cooler" temperatures. During February and March this species did not begin its daily aboveground activity until the soil surface temperature reached a mean of 56.1° C and the air temperature at ant height was 43.9° C. In mid-April the corresponding temperatures at first activity were approximately 4° C lower, but activity ceased for winter shortly thereafter. There is no evidence linking polymorphism in this species with its thermal biology.